Conventionally, as a valve device, there is known a valve device that includes: a poppet valve that is brought into and out of contact with a valve seat to open and close a flow path; a thread part that is formed on a shaft of the poppet valve; a driving gear into which the thread part is screwed; a pinion that engages with and rotates the driving gear; and driving means for rotationally driving the pinion, wherein the poppet valve is moved to advance or retreat depending on the rotational direction of the driving gear to control opening and closing of the flow path, by the driving means rotating the driving gear via the pinion (JP 2009-197765 A).
In this valve device, in order to prevent an impact from being transmitted to the motor serving as the driving means and the like when the poppet valve is seated on the valve seat, a required clearance (gap) is created between the thread part formed on the shaft of the poppet valve and a thread part of the driving gear, and, even when the poppet valve is seated on the valve seat and has stopped moving, the driving gear is allowed, when further rotated, to rotate to the extent of the clearance and absorb an impact that is applied to the driving means or the like.